Centrifugal gas sample cleaning system



June 28, 1966 E. L. WEISS 3,257,782

CENTRIFUGAL GAS SAMPLE CLEANING SYSTEM Filed Dec. 14, 1962 2 Sheets-Sheet l June 28, 1966 wE|$$ 3,257,782

CENTRIFUGAL GAS SAMPLE CLEANING SYSTEM Filed Dec. 14, 1962 2 Sheets-Sheet 2 United States Patent This invention relates to gas sample cleaning systems of the centrifugal type and has for an object the provision of an improved system employing a centrifugal cleaner which develops relatively high centrifugal forces for withdrawing a gas sample from a process, separating particulate matter from'the gas and discharging the particulate matter preferably to the process, the system being particularly suitable for use in connection with gas analyzers.

In accordance with one aspect of the invention, the system utilizes an improved apparatus for cleaning a gas sample. A continuous sample of dirty gas, that is to say a gas containing a large amount of particulate matter in the form of solids and possibly some liquid is drawn from a process to produce a gas sample stream which is conveyed to a chamber where the dirty gas is rotated about a central axis of the chamber to impart a centrifugal force thereto causing the gas and particulate matter to be thrown radially outward adjacent a coaxial wall of the chamber, A relatively clean gas sample stream is withdrawn by suction means located along said central axis. The degree of suction is such as to draw a fraction of the gas and lighter weight particulate matter inward toward the central axis This fraction of gas and particulate matter is then accelerated to a predetermined rotational velocity thus subjecting solid and liquid particles therein to a large centrifugal force due to the rotational motion as well as to centripetal forces due to viscous drag forces of the stream of gas being sucked inwardly toward the central axis. The dirt particles having a terminal velocity greater than the inward velocity of the gas sample stream are ejected in a radial direction While the stream of relatively clean gas is withdrawn along the central axis of the chamber. The foreign particles having the greater terminal velocity are exhausted from the chamber along with the uncleaned portion of the total gas sample stream.

Further in accordance with the invention, the centrifugal gas sample cleaning system includes a centrifugal cleaner unit having a blower wheel and a separator Wheel mounted closely adjacent each other on a common rotatable shaft within a housing. The shaft includes a hollow portion in communication with the interior of the separator wheel. Inlet means for connecting a sampling line to the centrifugal cleaner unit is provided adjacent the blower wheel. Means is also provided for connecting an excess sample discharge line with the outlet end of the cleaner unit and means is provided to connect a clean sample suction line with the hollow portion of the shaft for passage of cleaned gas therethrough.

Further in accordance with the present invention, the centrifugal cleaning system includes a post filter in the cleaned gas sample line to remove sub-micron sized particles. The post filter includes a cartridge wet with a liquid having a low vapor pressure such, for example, as polyethylene glycol. The cleaning system further includes means for draining condensed moisture from the cleaned gas sample line and pump means connected to the cleaned gas sample line to produce flow of the cleaned gas sample therethrough. In accordance with a further aspect of the invention, the means for draining condensed moisture from the cleaned gas sample line of the system includes a condenser and a water leg in the condensate drain line to prevent air from being sucked in with the cleaned gas sample. The height of the water leg may be used as a 3,257,782 Patented June 28, 1966 "ice measure of the degree of plugging of the filter and may therefore be used to provide a warning signal that the filter cartridge should be replaced.

For a more detailed description of the invention and for further objects and advantages thereof, reference is to be had to the following description taken in conjunction with the accompanying drawing in which:

FIG. 1 is a diagrammatic View of a centrifugal gas sample cleaning system embodying the present invention;

FIG. 2 is a schematic view illustrating the gas flow within the centrifugal gas sample cleaner of FIG. 1;

FIG. 3 is a schematic diagram of a warning signal arrangement for indicating the degree of plugging of the filter of FIG. 1; and

FIG. 4 shows a modification of sample cleaner of FIG. 1.

Referring to FIG. 1, the centrifugal gas sample cleaning system 10 embodying the present invention has been illustrated as including centrifugal cleaner unit 11 including a housing 12 at the opposite ends of which are provided connections for an inlet line or sampling probe 13 and an outlet line 14 which preferably will return excess sample to a process from which a sample of gas is taken The centrifugal cleaning unit ll includes a pair of blower wheels 16 and 17 of conventional construction, FIG. 2, mounted on a common shaft 18, the details of which will be further described later in connection with FIG. 2. The shaft 18 is provided with a flexible coupling 19, FIG. 1, which connects the centrifugal cleaner unit 11 to a drive motor 20. The drive motor 20 may be of any suitable type preferably having a speed in excess of 3,000 r.p.m. The cleaned gas leaving the cleaner unit 11 passes through a cleaned gas sample line 22 and into a filter 23 wherein sub-micron sized particles are removed. The cleaned gas then passes through a condenser illustrated as a coil, 24 and into a T connection 25, one opening of which is connected with a drain line 26 for removing condensed water from the sample before the clean gas sample enters a pump 28. The condenser and drain line provide means for lowering the sample dew point of the clean sample sufiiciently so that condensation will not occur in the sample transmission line 30 after it leaves the pump 28.

Having described the centrifugal gas sample cleaning system of this invention, certain portions thereof will now be described in more detail. the centrifugal cleaner in a preferred form-comprises a unit 11 of novel construction. Two blower wheels 16 and 17 are of identical construction being cup-shaped members having solid end Walls 16a, 17a. The sides of the cups projecting from the respective end walls 16a,

the centrifugal gas 17a include a plurality of closely spaced fins or blades,

16b, 17b. The first blower wheel 16 may be considered as a separator wheel and is mounted over av pair of openings 18a in shaft 18 which communicate with a hollow portion 1811 at the right-hand end of shaft 18 as shown in FIG. 2. The second blower wheel 17 may be referred to as an impeller wheel and-is mounted on the solid end of shaft 18 so that its solid back plate 17a serves to close off the open side of the cup-shaped separator wheel 16. The motor 20, FIG. 1, drives both of the wheels 16 and 17 at high rotational speed. The housing 12 provides a chamber for the gas sample. Dirt laden gas enters the chamber through line 13. The solid arrows 32 indicate the flow of. particulate matter of the gas sample and the dotted arrows 32g indicate the flow of the gaseous portion thereof produced by the rapidly rotating impeller wheel 17. The impeller wheel 17 draws a relatively large excess of dirty gas sample from a process stream and the excess sample is blown back into the process stream. The total sample enter-.

Referring to FIG. 2,

and the excess sample leaving the cleaner, indicated by the arrows 33 and 33g, is blown back into the process stream by way of line 14.

As may be seen in FlG. 2, the sample components indicated by the solid arrows 32 for particulate matter and the dotted line arrows 32g for gas are drawn into the centrifugal cleaner unit 11 from the inlet line 13 by the impeller blower wheel 17. This sample is rotated about the axis of shaft 18 and a centrifugal force is imparted to the sample thereby causing it to be thrown radially outwardly against the wall of housing 12. Suetion is applied to the hollow portion 18b of shaft 18 by the pump 28, FIG. 1, thus drawing a small fraction of the lighter weight components of the total sample inwardly through the periphery of the separator wheel 16, FIG. 2. This fraction of the gas sample entering the wheel 16 at its periphery is accelerated to the rotational velocity of the separator wheel 16 and any solid or liquid particles in this fraction of the gas sample are thus subjected to the centrifugal forces due to the rotational motion as well as centripetal forces due to viscous drag forces of the inward moving fraction of the gas sample. Particles having a mass which is large compared to that of the sample gas molecules are prevented from entering the separator wheel 16, hence these particles pass through the unit 11 along with the excess sample as indicated by the broken lines 33, 33g, FIG. 2, and out through the return pipe 14. A fraction of the gas sample 330 is thus rendered clean and such clean sample is exhausted through the openings 18a, hollow shaft portion 18!), openings 18c, chamber 34, and line 22.

The centrifugal force on a particle is proportional to its mass, its distance from the center of rotation and the square of its angular velocity about the center of rotation. The centripetal force is proportional to gas viscosity, particle size and relative velocity of gas and particle. For small particles, a limiting or terminal velocity relative to the gas is quickly reached. Particles will be ejected from the separator wheel 16 if this terminal velocity is greater than inward velocity of the gas. In general, the large dense particles will be ejected while the small, less dense particles are carried along with the gas sample. The limiting combination of size and density a particle must have in order to be separated from the fraction of the gas sample which is to be cleaned will depend on the sample viscosity, the required sample flow rate, and the separator wheel size, velocity, and face area.

I portion of the sample.

inserted in a water reservoir 36, and the lower end of drain line 26 is maintained below the surface of the water. The height of the water leg within the drain line 26 obviously will depend upon the suction in the sample line. This suction will vary in time due to gradual plugging of the filter 23. The height of the water leg may therefore be used to detect the degree of plugging that has occurred in the filter and may be used as an indication that the filter cartridge 23a should be replaced.

A signal may be provided as a warning that the filter cartridge 23a should be replaced by placing electrodes in the condensate drain line 26 above the normal water level as indicated in FIG. 3. Increased suction will cause a rise in water level in drain line 26 bringing the condensate up to a material, r is the particle radius, and 1 the viscosity of the gas. Taking R=6 cm. and N=60/sec., as an example, then by substitution,

Using this value for acceleration, the value for viscosity of air (l.8 10- and the density of Water, 1.0, the terminal velocity may be calculated as a function of particle radius:

1) 2 8.55 X10 1.Or

If r is expressed in microns instead of centimeters this expression becomes v=l0.5r cm./sec. Only particles for which this value is smaller than the gas velocity into the separator wheel will be carried along with the cleaned A commonly used sampling rate of 235 cc./sec. requires a sample velocity of 1.3 cm./sec. through the periphery of the separator wheel. Thus it is seen that particles of density 1.0 and radius smaller than about /3 micron will not be separated.

Because particles of smaller size than the foregoing are expected in some processes, a filter 23, FIG. 1, is added. To remove sub-micron sized particles efficiently, a filter of the wet cartridge type is preferably employed. An example of a suitable filter of this type is a model B4BD Fulfio filter sold by Commercial Filters Corporation, Melrose, Massachusetts. This model utilizes a cotton cartridge. It is desirable to wet the cartridge thoroughly with a liquid having a low level which permits electrical current flow between the electrode with the condensate forming the current path. Placing an addi- 1.05 b cm./scc.

, tional electrode at a higher position in the drain line 26 The relative motion of dirt particles may readily be Q calculated. The centrifugal acceleration of the particles is given by Equation 1:

where a is the acceleration, d is the density of the particle vapor pressure prior to use. liquid is polyethelene glycol having a molecular Weight of 300.

As illustrated in FIG. 1, provision has been made for lowering the sample dew point of the cleaned sample so that condensation will not occur in the sample transmission lines. After the cleaned sample leave-s the filter 23, it passes through a condenser 24 illustrated as a coil of copper tubing inserted in the sample line between the filter 23 and the drain T 25. The T connection 25 is used for draining condensed water from the sample before it enters the pump 28. A water leg is required in the condensate drain line 26 to keep air from being sucked into the sample. Thus, the lower end of drain line 26 is An example of a suitable so that a second electrical circuit is completed by further rise in water level may be used to provide means for stopping the sample pump 28 if. the warning provided by the first current path closure has not been heeded in time. S0 or CO in the sample gas will dissolve in the condensate draining through line 26 thus assuring adequate conductivity of the water in the water leg. The cleaned gas sample line 22a is connected to the side of the T fitting 25 whereas the other connections to it are made with the condensate drain line 26 at one end and the line 22b going to the suction side of pump 28 at the other. The pump 28 is illustrated in FIG. 3 as being driven from an electric motor M which is energized from a suitable source of power through normally closed contacts of a relay 40. The drain line 26 is of conductive material which is shown divided into a plurality of sections such as 26, 26a, 26b with sections 26 and 26a being joined by an electrical insulating sleeve 41 and sections 26a and 26b being joined by an electrical insulating sleeve 42. The section 26a of the drain line serves as a common electrode which is connected by way of conductor 43 to one side of a secondary of isolating transformer 44. The other side of the secondary of transformer 44 is connected to drain line section 26 and section 261) respectively through the coils of relays 49 and 45. As the height of the water rises in drain line section 26b, it will bridge the insulating segment 42 completing a circuit from transformer 44 through the common electrode 26:: thus energizing the coil of relay 45 and causing its normally open contacts to move to closed position thereby completing the electrical circuit for the warning light 47 and/ or horn 48. When the water within the drain line rises sufiiciently high to engage the lower end of pipe section 26, FIG. 3, the circuit will be completed between electrode 26a and 26 thereby energizing the coil of relay 40 causing its normally closed contacts to be opened and thus interrupting the power to motor M and stopping sample pump 28.

By way of example a centrifugal gas sample cleaning system embodying the present invention had a centrifugal cleaner unit containing impeller and separator wheels driven by a 3450 r.p.m. motor. The sample inlet line 13 and excess sample return line 14 were conventional l" i.p.s. wrought iron pipe. The cleaned gas sample line 22 and subsequent sample transmission line sections 22a, 22b and 30 were A" copper. It is to be understood that the blower wheels may be equipped with inserts to reduce the internal volume of the cup-shaped wheels to reduce the inactive volume of the blower thereby to reduce sampling lag.

FIG. 4 illustrates diagrammatically an additional modification of the centrifugal cleaner unit 11 shown in the system of FIGS. 1-3. The centrifugal gas cleaner unit 111 of FIG. 4 may be inserted in the system of FIG. 1 in place of the unit 11. As will be seen, the unit 111 includes a housing 112 at the opposite ends of which are provided connections for the inlet line 13 and the outlet line 14 which returns excess sample to the process. The centrifugal cleaning unit 111 includes two blower wheels 116 and 117, the wheel 117 being of larger diameter than the wheel 116 so that the latter can be inserted within the wheel 117. The larger blower wheel 117 acts as an impeller wheel while the smaller blower wheel 116 acts as a separator wheel. The wheels 116 and 117 are associated in face to face relation on the shaft 118 so that the solid back 117a of wheel 117 closes off the open side of the cup-shaped separator wheel 116. The back 116a of wheel 116 is positioned adjacent the open end of wheel 117. The gas sample flow through the unit 111 is similar to that described above in connection with unit 11,- FIG. 2, with the clean gas passing through the openings 11811 at the hollow end 1181) of shaft 118 and out through the outlet openings 1186- to the clean gas line 22.

From the foregoing description, it will be seen that the modification shown in FIG. 4 of the centrifugal unit 111 may be utilized in the system shown in FIG. 1 in place of the unit 11. The remaining'portions of the system such as the filter, condenser and pump will be the same. It will also be understood that the warning system of FIG. 3 is adapted for use with the centrifugal cleaner unit 111 of FIG. 4. While the embodiment illustrated in FIG. 2 of the centrifugal cleaner unit 11 is preferred, it is to be understood that other modifications such as unit 111 of FIG. 4 will operate satisfactorily in the system of FIG. 1. It is also to be understood that the units 11 and 111 may be operated in either horizontal or vertical positions.

It is to be understood that the invention is notlimited to the specific arrangements described and illustrated and that other modifications thereof may be made within the scope of the appended claims.

What is claimed is:

1. A centrifugal gas sample cleaning system comprising a centrifugal cleaner unit including a housing having an inlet means for connecting a sampling line to the inlet end of said housing of said centrifugal cleaner unit adjacent said blower wheel,

means for connecting an excess sample discharge line with the outlet end of said housing of said cleaner unit,

means for connecting a cleaned gas sample suction line with said hollow portion of said common rotatable shaft for passage of cleaned gas therethrough, a

filter in said cleaned gas sample line to remove submicron size particles,

means for condensing moisture and means for draining condensed moisture from said cleaned gas sample line,

said means for draining condensed moisture from said cleaned gas sample line including a water leg connected in said line downstream from said condensing means,

said water leg comprising a drain line having its lower end immersed below the liquid level of a water reservoir,

said drain line including at least three electrical contacts one above the other which are interconnected by electrical insulating sections with pairs of contacts adapted to be bridged by electrically conductive liquid in said water leg dependent upon the level thereof, one of said contacts effective as a common contact in an electrical circuit, the other contacts forming separate contacts in said electrical circuit,

first relay means in circuit with the lower pair of said contacts and second relay means in circuit with the upper pair of said contacts,

said first relay means having normally open contacts a in electrical circuit with a warning signal means, and said second relay means having normally closed contacts in circuit with an electrical motor.

2. A centrifugal gas sample cleaning system comprising a centrifugal gas sample cleaner,

a cleaned gas sample line for passage 'of cleaned gas from. said cleaner,

a filter in said cleaned gas sample line downstream of said cleaner to remove sub-micron size particles,

a gas sample pump downstream of said filter having its suction side connected to said cleaned gas sample line,

means connectedto said cleaned gas sample line be tween said filter and said pump for lowering the sample dew point of the cleaned gas sample so that condensation will not occur in a sample transmission line leading from said pump,

. said last-named means including a liquid leg having a drain line with its lower end immersed below the liquid level of a body of liquid in a reservoir for draining condensed moisture from said cleaned gas sample line while preventing air from being sucked into said cleaned gas sample line by said pump, and

means responsive to the height of the liquid in said liquid leg to provide a warning signal as to the degree of plugging of said filter.

3. In a centrifugal gas sample cleaning system according to claim 2 wherein said responsive means includes at least three sections in said drain line which are interconnected by electrical insulating sleeves, the center one of said sections forming a center electrode in an electrical circuit, the end sections forming separate electrodes in said electrical circuit, first relay means in circuit with the lower one of said end electrodes, and second relay means in circuit with the upper one of said electrodes, said first relay means having normally open contacts in electrical circuit with a warning signal means, and said second relay means having normally closed contacts in circuit with an electrical motor connected to and for operating said pump.

4. A centrifugal gas sample cleaner comprising a housing having a single chamber defined by a side wall and end walls respectively at opposed inlet and outlet ends thereof,

' means for feeding sample gas to said inlet end of said chamber,

.a shaft rotatably mounted in said end walls and extending through said chamber,

means for rotating said shaft,

wheel structure comprising impeller means and separator means mounted on said shaft within said chamber,

said wheel structure including disc means afiixed on said shaft for rotation therewith,

said disc means comprising a pair of solid plates coaxially mounted on the shaft and spaced from each other in the axial direction of the shaft,

said impeller means comprising a first plurality of closely spaced blades having ends afiixed adjacent an outer periphery of a first of said plates and having the opposite ends extending therefrom in the axial direction of the shaft towards the inlet end of said chamber and free of the second plate to provide an open end for said impeller means to draw a gas sample into saidchamber,

said means for feeding sample gas to said inlet end of the chamber including means for axially directing the sample gas towards the open end of the impeller means,

said separator means comprising a second plurality of closely spaced blades supported by said disc means and positioned between said pair of plates with the last-named blades located adjacent the outer periphery of the second of said plates and extending therefrom in the axial direction of the shaft to produce radially outward forces on the gas sample'received by said separator means from said impeller means,

said first and second plurality of blades being radially spaced from the shaft and the side wall of said chamber and circumscribing a pair of annular spaces between themselves and said shaft,

said pair of plates being constructed and arranged to provide axially spaced end closure means for the annular space circumscribed by said second plurality of blades of said separator means,

at least a portion of the length of said shaft being hollow and having inlet port means encircled by the annular space circumscribed by said second plurality of blades of said separator means,

means for connecting a cleaned gas suction line to the hollow portion of said shaft, and

means adjacent the outlet end of said chamber for removal of excess sample gas from the space between said blades and the side wall of the chamber.

5. A centrifugal gas sample cleaner as claimed in claim 4 wherein said impeller means and said separator means are arranged serially on said shaft.

6. A centrifugal gas sample cleaner as claimed in claim 4 wherein said separator means and said impeller means are arranged concentrically on said shaft with said first plurality of blades circumscribing said second plurality of blades.

7. In the combination claimed in claim 4,

a cleaned gas suction line connected to the means for connecting the same to said hollow portion of said shaft,

and a filter in said cleaned gas suction line including means to remove sub-micron size particles.

8. In the combination claimed in claim 7,

means for condensing and draining condensed moisture from said cleaned gas suction line,

and pump means connected to said cleaned gas suction line,

said filter, said condensing and draining means and said pump means being serially connected.

References Cited by the Examiner UNITED STATES PATENTS 978,450 12/1910 Homans. 1,554,726 9/ 1925 Hoffman 55-403 2,187,066 1/1940 Youker 55-400 2,361,758 10/1944 De Fligue 55-315 X 2,443,875 8/1948 Spangenberger 55-410 2,457,903 1/1949 Kantor et al 55-165 2,556,832 6/1951 Vollrath 55-270 X 2,661,076 12/1953 Walker 55-404 2,687,185 8/1954 McChesney 55-80 2,737,857 3/1956 Lee 55-199 2,923,151 2/1960 Engle et a1. 55-199 3,018,896 1/1962 Gewiss 55-400 X 3,070,990 1/1963 Krinov 55-270 3,094,106 6/1963 Hyman 73-304 3,098,819 7/1963 Sager 210-97 3,100,347 8/1963 Fritze 73-304 3,103,002 9/1963 Pearson 73-304 3,105,749 '10/1963 Gebert et a1. 55-208 3,111,031 11/1963 Kuritza 73-304 FOREIGN PATENTS 52,897 6/1944 France.

9,618 1914 Great Britain.

REUBEN FRIEDMAN, Primary Examiner.

B. NOZICK, Assistant Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 ,257 ,782 June 28 1966 Edward L. Weiss It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 4, line 16, beginning with "material, r is the" strike out all to and including "having a low", in line 45, and insert the same after "particle" in column line 61.

Signed and sealed this 24th day of October 1967.

(SEAL) Attest:

Edward M. Fletcher, Jr. EDWARD J. BRENNER Attesting Officer Commissioner of Patents 

4. A CENTRIFUGAL GAS SAMPLE CLEANER COMPRISING A HOUSING HAVING A SINGLE CHAMBER DEFINED BY A SIDE WALL AND END WALLS RESPECTIVELY AT OPPOSED INLET AND OUTLET ENDS THEREOF, MEANS FOR FEEDING SAMPLE GAS TO SAID INLET END OF SAID CHAMBER, A SHAFT ROTATABLY MOUNTED IN SAID END WALLS AND EXTENDING THROUGH SAID CHAMBER, MEANS FOR ROTATING SAID SHAFT, WHEEL STRUCTURE COMPRISING IMPELLER MEANS AND SEPARATOR MEANS MOUNTED ON SAID SHAFT WITHIN SAID CHAMBER, SAID WHEEL STRUCTURE INCLUDING DISC MEANS AFFIXED ON SAID SHAFT FOR ROTATION THEREWITH, SAID DISC MEANS COMPRISING A PAIR OF SOLID PLATES COAXIALLY MOUNTED ON THE SHAFT AND SPACED FROM EACH OTHER IN THE AXIAL DIRECTION OF THE SHAFT, SAID IMPELLER MEANS COMPRISING A FIRST PLURALITY OF CLOSELY SPACED BLADES HAVING ENDS AFFIXED ADJACENT AN OUTER PERIPHERY OF A FIRST OF SAID PLATES AND HAVING THE OPPOSITE ENDS EXTENDING THEREFROM IN THE AXIAL DIRECTION OF THE SHAFT TOWARDS THE INLET END OF SAID CHAMBER AND FREE OF THE SECOND PLATES TO PROVIDE AN OPEN END FOR SAID IMPELLER MEANS TO DRAW A GAS SAMPLE INTO SAID CHAMBER, SAID MEANS FOR FEEDING SAMPLE GAS TO SAID INLET END OF THE CHAMBER INCLUDING MEANS FOR AXIALLY DIRECTING THE SAMPLE GAS TOWARDS THE OPEN END OF THE IMPELLER MEANS, SAID SEPARATOR MEANS COMPRISING A SECOND PLURALITY OF CLOSELY SPACED BLADES SUPPORTED BY SAID DISC MEANS AND POSITIONED BETWEEN SAID PAIR OF PLATES WITH THE LAST-NAMED BLADES LOCATED ADJACENT THE OUTER PERIPHERY OF THE SECOND OF SAID PLATES AND EXTENDING THEREFROM IN THE AXIAL DIRECTION OF THE SHAFT TO PRODUCE RADIALLY OUTWARD FORCES ON THE GAS SAMPLE RECEIVED BY SAID SEPARATOR MEANS FROM SAID IMPELLER MEANS, SAID FIRST AND SECOND PLURALITY OF BLADES BEING RADIALLY SPACED FROM THE SHAFT AND THE SIDE WALL OF SAID CHAMBER AND CIRCUMSCRIBING A PAIR OF ANNULAR SPACES BETWEEN THEMSELVES AND SAID SHAFT, SAID PAIR OF PLATES BEING CONSTRUCTED AND ARRANGED TO PROVIDE AXIALLY SPACED END CLOSURE MEANS FOR THE ANNULAR SPACE CIRCUMSCRIBED BY SAID SECOND PLURALITY OF BLADES OF SAID SEPARATOR MEANS, AT LEAST A PORTION OF THE LENGTH OF SAID SHAFT BEING HOLLOW AND HAVING INLET PORT MEANS ENCIRCLED BY THE ANNULAR SPACE CIRCUMSCRIBED BY SAID SECOND PLURALITY OF BLADES OF SAID SEPARATOR MEANS, MEANS FOR CONNECTING A CLEANED GAS SUCTION LINE TO THE HOLLOW PORTION OF SAID SHAFT, AND MEANS ADJACENT THE OUTLET END OF SAID CHAMBER FOR REMOVAL OF EXCESS SAMPLE GAS FROM THE SPACE BETWEEN SAID BLADES AND THE SIDE WALL OF THE CHAMBER. 